Search warrants served at three Humboldt County properties Monday by the Humboldt County Sheriff's Office Community Response Unit following a month-long investigation led to the arrest of a father, mother and son -- and the discovery of hundreds of growing marijuana plants and numerous firearms.

According to a press release, CRU deputies, assisted by Humboldt County Drug Task Force agents, served the first warrant on the 2100 block of Law Boulevard in Eureka at about 7:30 a.m. Upon arrival, deputies met with 19-year-old Matthew Mildbrandt and a 17-year-old female. While searching the residence, deputies located 10 1-pound packages of marijuana bud, an assault weapon, 65 growing marijuana plants, about 10 pounds of processed marijuana, a U.S. Postal Service parcel containing about 2 pounds of processed marijuana ready to be shipped, paperwork indicating marijuana sales and about $6,000 in cash. Deputies also found evidence of Mildbrandt having unlawful sexual relations with a minor, the release said.

Mildbrandt was arrested on suspicion of possession for sale of marijuana, conspiracy to commit a felony, being arrested in commission of a felony and unlawful sexual relations with a minor. He was booked into the Humboldt County jail. His bail is set at $50,000.

The juvenile female was released to her mother.

Deputies Monday later served the second search warrant at a residence on the 1900 block of Scenic Drive in Fortuna belonging to 56-year-old Mark Mildbrandt and 54-year-old Denise Mildbrandt, the parents of Matthew Mildbrandt. Neither parent was at the residence when deputies arrived.

While searching the residence, deputies found 19 firearms, including two assault weapons, and paperwork indicating sales of marijuana. They also found over 400 ounces of silver, along with other precious metals, and about $13,000 in cash.

While deputies were at the home, Mark Mildbrandt arrived in his employer's truck. A search of the vehicle revealed about 10 pounds of harvested marijuana.

Mark Mildbrandt was arrested on suspicion of cultivation and possession of marijuana for sale, conspiracy and being armed in commission of a felony. He was booked into the Humboldt County jail. His bail is set at $50,000.

Denise Mildbrandt arrived at the residence after Mark Mildbrandt. She was arrested on suspicion of cultivation and possession of marijuana for sale, conspiracy and being armed in commission of a felony. She was booked into the Humboldt County jail. Her bail is set at $50,000.

Based on information discovered while deputies searched the residence of Mark and Denise Mildbrandt, a search warrant was obtained for property on the 2500 block of Burr Valley Road in Dinsmore believed to be owned by all three Mildbrandts. Deputies driving to the property at about 4 p.m., discovered that four fir trees had recently fallen across the road, blocking the deputies from accessing the property. The fallen trees also blocked non-involved residents from accessing or leaving their homes. After about 30 minutes of chainsaw work, deputies were able to clear the road enough to pass.

Upon arrival at the property, deputies located a log cabin that had been converted for the purpose of marijuana cultivation, the release said. No one else was present. The cabin including a small living space, as well as a drying and manicuring room. A diesel-powered greenhouse that had leaked several gallons of diesel and oil onto the ground was also located. In the greenhouse, the release said, deputies discovered 300 growing marijuana plants about 1 foot tall, 364 pounds of dried marijuana and three firearms, including a shotgun.

The Humboldt County Code Enforcement Unit and the Humboldt County Division of Environmental Health are being notified of the environmental damage that the deputies witnessed, the release said.